How do I space quads evenly?
Select the inner Vertices, press W > Smooth and adjust Smooth Vertex settings:



You can also access Smooth Vertex operator settings via F6:



Another way is selecting a whole row or column of vertex and then Scale in X or Y axis to a factor or Zero with S > X + 0

Alternatively place the 3D cursor over the vertex you wish to align to, press . to transform relative to the 3D Cursor position, and then repeate the scale process described above. S > X + 0